Computerized systems for operating on color images are known in the art. Some of these systems scan color films or prints to produce digital color images; other systems provide tools for directly generating the digital color images. An example of such a system is the Whisper workstation manufactured by Scitex Corporation Ltd. of Herzlia, Israel.
The digital color images thus produced can be modified in any of a number of different ways, typically on a color electronic preptess system (CEPS). The CEPS enables a user to change some or all of the colors of the image, to mask out sections of the image, to clip the image, etc.
Typically, the user changes the image until it achieves an aesthetically pleasing appearance, at which point, the user saves the modified image and/or provides it to a printing device, such as a color proofer, an example of which is the 3024 proofer manufactured by Iris Graphics Inc. of Bedford, Mass., U.S.A.
The user typically modifies the image with an expectation that what he sees on the monitor of the CEPS will be reproduced exactly on the output medium of the proofer. Due to the nature of color and color reproduction, the proofer rarely can exactly reproduce the color produced on the monitor.
The above problem occurs because a number of color coordinate systems are utilized in the process of preparing and reproducing a color image. Specifically, the digital color images are typically represented in a first color coordinate system of the scanner or image generation system, typically based on a Red-Green-Blue (RGB) separation of visible light. They are displayed on the monitor of the CEPS or image generation system in a second RGB color coordinate system.
The modified image, in the first RGB color coordinate system, is provided to an output device which converts the image into an output color coordinate system, typically based on a Cyan-Magenta-Yellow-Black (CMYK) separation of printing inks. The CMYK color coordinate system of the output device is dependent on the colors of its inks and therefore, the reproductions of the same modified image on two different devices look different.
The following terms are defined:
The term "color coordinate system" refers to three or more orthogonal axes used to define a color. Example color coordinate systems are RGB, CMYK, neither of which have been defined by a standard, and which is a standard color coordinate system. PA1 A "color space" is the three-dimensional space in which each point corresponds to a color. PA1 A "colorimetric color coordinate system" is one that attempts to define colors as they are perceived by humans. Mathematical differences between colors in such a color space can be related to perceptual differences between colors with some consistency.
Many systems have been designed to produce color matches between a display and a printed output. U.S. Pat. No. 4,500,919 to Shreiber describes a color reproduction system that maintains the images within colorimetric color coordinate systems that are defined according to international standards. Because the color coordinate system of the digital image, the monitor and the printer are all colorimetric, the printed output should match the input image and the image as displayed on the screen.
U.S. patent application Ser. No. 749,299 assigned to the present assignee, now U.S. Pat. No. 5,315,380 describes a color conversion system for matching output of a proofer with output of a photomechanical proofing process.
U.S. patent application Ser. No. 640,468, assigned to a related company of the present assignee, describes a color conversion system for matching the output of two types of printing devices.